Wave guide junction matching device



March 15, 1955 R. H. DICKE 2,704,351

WAVE GUIDE JUNCTION MATCHING DEVICE Original Filed March 8, 1945 2Shee'ts$heet l INVEN TOR. fiqZeri f2! Dic/re ATTOR/VH March 15, 1955 R.H. DICKE 2,704,

WAVE GUIDE JUNCTION MATCHING DEVICE Original Filed March 8, 1945 2Sheets-Sheet 2 F gl 6;

INVENTOR. fioberi' l1. Die/re United States Patent WAVE GUIDE JUNCTIONMATCHING DEVICE Robert H. Dicke, Cambridge, Mass., assignor to theUnited States of America as represented by the Secretary of War Originalapplication March 8, 1945, Serial No. 581,695,

now Patent No. 2,593,120, dated April 15, 1952. Digisdzeg and thisapplication March 19, 1952, Serial No.

1 Claim. (Cl. 333-11) This application is a division of applicationSerial No. 581,695 entitled Transmission Systems, which was filed March8, 1945, and issued April 15, 1952, as Patent No. 2,593,120.

This invention relates to transmission systems and more particularly toan impedance transformer for use with ultra high frequency energy.

According to conventional theory the dominant mode of operation of awave guide may be defined as that condition of operation in which theconfiguration of electric and magnetic lines of force permits thetransmission of energy at the lowest possible frequency through a waveguide of a given size and geometric cross-section. It may also bedefined with equal accuracy as that condition of operation in which theconfiguration of electric and magnetic lines of force permits thetransmission of energy through the smallest dimensional wave guide of agiven cross-section at a given frequency.

In a rectangular wave guide operated in the dominant mode, there existsa sinusoidal distribution of electric lines of force along the majoraxis of the rectangular cross-section. These electric lines of force orelectric field vectors are perpendicular to the major axis of therectangle.

When a main rectangular wave guide designed to be operated in thedominant mode is joined symmetrically by a wave guide whose axis isparallel to the electric field vectors in the main wave guide, thejuncture is said to be a series junction. When the joining wave guide issymmetrical to a main wave guide and the axis of the joining guide isperpendicular to the electric field vectors within the main guide, thejunction is said to be a parallel junction. When these two junctures,one series and one parallel, are made in such a manner that the axes ofthe series and parallel wave guides join the axis of the main wave guideat the same point certain unique properties exist. Broadly, anygeometric arrangement of four wave guide branches will also give theseunique properties if the following conditions are met. The axes of thefour guides must meet at a common point. In a first and second of theseguide branches the electric lines of force are perpendicular to eachother and the lines of force in one of these first and second wave guidebranches must be perpendicular to a plane passing through the axes ofthe first and second wave guide branches. The third and fourth of thesewave guide branches must be symmetrical with respect to the planepassing through the axes of the first and second wave guide brancheswhich was just referred to. These unique properties are explainedfurther in the detailed discussion of the drawings. It will beappreciated, however, by those skilled in the art that where any abruptchange in structure occurs, mismatch and consequent undesirablereflections also tend to occur. This is especially so where one waveguide branches into two or more wave guides. When a wave guide isterminated in its characteristic impedance, no mismatch or reflectionswill occur. The desirability of the unique properties referred to aboverender it advisable to eliminate tthe unwanted mismatch and reflections.

In certain radio communication systems a common radiating and receivingdevice, or antenna, is used for transmitting and receiving and in suchsystems a part of the channel for transmitted energy is common to a partof the channel for the received energy. There then exists the problem ofpreventing the transmitted energy,

2,704,351 Patented Mar. 15, 1955 which is of normally higher level, frombeing partly' spent in the receiver channel and damaging the receivingdevice. Conversely, there exists the problem of preventing the receivedenergy of normally lower level from being wasted in the transmitterchannel. In certain cases it is absolutely essential that thetransmitted power be eliminated or at least minimized, from thereceiver. A system of transmit-receive or T-R devices were made toachieve this purpose. However, there still existed at least two sourcesof trouble. The first was that an initial high level transmitted energyspike managed to escape the action of the T-R device and the second wasthat the T- R device was not capable of excluding from the receivmgdevice a low level or plateau of energy.

Many methods have been employed in the past for matching or transformingone impedance to another. At the lower radio frequencies this is donewith lumped circuits such as transformers or with line stubs such as thedouble stub tuner. For radio frequencies sufiiciently high to warrantthe use of wave guides these stub tuners can still be used but withincreasing difficulty. Impedance transformers with greater range ofmatching and ease of operation are desirable.

Oftentimes in radio work it is desired to variably attenuate or reduce asignal in magnitude. At low radio frequencies the problem is simple, butat frequencies for which wave guides are practical the problem of avariable attenuator becomes quite complex.

One object of this invention is, therefore, to terminate each wave guideat its junction with other wave guides in its characteristic impedance.

A further object of this invention is to provide a system for permittingenergy to flow to and from a common element through a common channelwith no coupling between the sending and the receiving elements whichare located at the same end of the common channel.

Still another object of this invention is to match or transform oneimpedance into another.

A still further object of this invention is to provide a variableattenuator, capable of handling large amounts of power, using matchedwave guide junctions.

In accordance with the present invention there is provided a matchedjunction formed by three wave guides. One of the three wave guides isjoined to a second of the three wave guides in a series junction. Thethird wave guide joins the second wave guide in a parallel junction. Aniris, for matching purposes, is inserted in the second wave guide. It ismounted in such a position as to lie in a plane which also contains theaxes of the first and third wave guides. A second iris is located withinthe first wave guide. The two irises are so adapted that each wave guidesees as its termination at the junction its characteristic impedance.

For a better and fuller understanding of the invention, together withother objects thereof, reference is made to the following detaileddescription taken in connection with the accompanying drawings in which:

Fig. 1 shows an improved wave guide junction;

Figs. 2, 3, and 4 show views looking into different wave guides makingup the junction of Fig. l to show the position of matching irises;

Figs. 5A, 5B, 5C, and 5D facilitate describing some of lt he uniqueproperties of the matched junction shown in ig. 1;

Fig. 6 shows an improved transmission system;

Fig. 7 shows an improved impedance transformer; and

Fig. 8 shows an improved variable attenuator system.

Referring now more particularly to Fig. 1, there is shown a matchedjunction formed by three wave guides. A first wave guide with twobranches 11 and 12 is joined by a second wave guide 13, symmetrically ina series connection. A third wave guide 14 is joined symmetrically andin a parallel connection to the first wave guide 11-12. The series andparallel junctions are so made that the axes of the first, second, andthird wave guides meet in a point. Fig. 1 shows the wave guides 13 and14 as being perpendicular to the wave guide 11-12. While this is apreferred embodiment, it is not desired to limit the invention heredescribed to this geometric arrangement. Two irises 15 and 16,preferably in the form of thin plates of conducting material, areinserted at the junction to permit matching of all four wave guidebranches, that is to say, looking from any one of the four wave guidebranches toward the junction each of the wave guide branches will beterminated by its characteristic impedance. Fig. 2 shows the iris 15partially closing oif wave guide branch 11 as it is viewed from line 22in Fig. 1. In Fig. 3 this same iris 15 is shown as it is viewed fromline 33 in Fig. 1. Fig. 4 again shows the iris 15 as it is viewed fromline 4-4 in Fig. 1. Figs. 2, 3, and 4 taken together show the iris 15 tobe within the wave guide 11-12 and to lie in a plane which includes theaxes of wave guides 13 and 14. By variation of the length 17 and thedepth 18 of the iris 15 shown in Fig. 2, the iris 15 is adjustedempirically so that the third branch 14 is terminated in itscharacteristic impedance. Fig. 4 also shows the position of the iris 16.Figs. 2 and 4 taken together show the iris 16 to be within the waveguide 13. By variation of the length 19 of the iris 16 (Fig. 4) and theaxial distance 20 of the iris 16 from the junction (Fig. 3), the iris 16is adjusted empirically so that the second branch 14 is terminated inits characteristic impedance.

Referring now to Figs. A, 5B, 5C, and 5D specifically, there is shownfour novel ways in which the matched junction of Fig. 1 operates.Although there are other novel modes in which a junction, such as isillustrated in Fig. 1, operates, the modes illustrated in Figs. 5D5Dinclusive are deemed sufiicient for explanatory purposes. In Fig. 5Aenergy P, which enters the parallel connected wave guide 14, divides atthe junction into the two branches 11 and 12 of main wave guide. Theenergy divides equally, and the two parts are in phase with each otheras indicated by the designation +(P/2) at the ends of each of wave guidebranches 11 and 12. In Fig. 5B the converse of the condition illustratedin Fig. 5A is shown. If energies of equal magnitude and similar phase+(P/2) enter the two branches 11 and 12 of the main wave guide, theseenergies combine at the junction, and all of this energy enters theparallel connected wave guide 14 and is designated by P. In Fig. 5C isshown the condition where energy P enters the series connected waveguide 13. This energy divides equally and passes into the two branches11 and 12 of the main guide. The two energies will be in 180 phaseopposition as shown by the designation (P/2) at the end of guide branch11 and the designation +(P/ 2) at the end of guide branch 12 in thisfigure. Fig. 5D shows the converse of the condition shown in Fig. 5C. Ifenergies of equal magnitude and in 180 phase opposition as indicated by-(P/2) and +(P/2), the energies will combine and will all enter theseries connected wave guide 13. This energy is designated by P. To thoseskilled in the art, it will be obvious that energies which enter the twobrancahes of the main guide but which are neither in phase nor in phaseopposition will be combined and will divide going into both the seriesand the parallel connected wave guides. The relative division into theseries and parallel connected wave guides will be a function of thephase relation existing between the two energies. This will be readilyseen when one considers that either energy may be resolved into twocomponents, one component in phase and one component in phase oppositionto the other energy.

In Fig. 6 there is shown a novel apparatus employing the matchedjunction of Fig. 1 in a wave guide circuit. This is the preferredarrangement. However, the circuit will function if unmatched junctionsare used. A transmitter or transmitting device 41 is connected to a waveguide 42. Wave guide 42 comprises the series connected branch of a firstmatched junction 43. The parallel connected wave guide 46 of thisjunction 43 is connected to a radiating device 62. The branches 44 and45 of the junction 43 are connected, respectively, to the branches 47and 48 of a second matched junction 53. The electrical length of waveguide 44-47 from the junction 43 to the junction 53 differs from theelectrical length of wave guide 45-48 from the junction 43 to thejunction 53 by an integral number of wave lengths. Integral number istaken to include zero. The series connected wave guide 54 of the secondmatched junction 53 is terminated in an absorptive load 55. The parallel connected wave guide 56 of the second matched junction 53 goes toa receiving device 61. Two T-R devices 51 and 52 are inserted in the twowave guides 44--47 and 45-48. Their electrical distances from thejunction 43 difier by an odd number of quarter wavelengths. Atransmit-receive (T-R) device may be defined for the purposes of thisinvention as a device operative only by high level energy and which whenoperative will cause a maximum of reflection of the high level energy tooccur. Low level energy such as received signals will not operate theT'R device and so will continue past the device unaltered.

A detailed description of the operation of the apparatus of Fig. 6follows. The transmitter 41 is connected to feed energy into theapparatus through wave guide 42. Referring to Fig. 5C, we note that thisenergy will divide at the matched junction 43 equally, going into waveguide 44 and wave guide in 180 phase opposition with no energy passingdirectly into wave guide 46. The energy of high level transmission willbreak down the T-R devices 51 and 52, but both relatively short highlevel energy and relatively long low length energy which escapes theaction of the T-R devices continue past the T-R devices 51 and 52 withno phase change and reach the matched junction 53. The path fromjunction 43 through wave guide 44-47 to junction 53 being equal inelectrical length to the path from junction 43 through wave guide 45-48to junction 53, and since the energy in these two paths leaves junction43 in 180 phase opposition, the energy in these two paths arrives at thematched junction 53 in 180 phase opposition. Referring to Fig. 5D, wenote that this energy will all pass into wave guide 54 and be absorbedby the matched load 55. It is to be noted that no energy from either therelatively short high level portion or the relatively long low levelportion passes into the wave guide 56 and receiving device 61. Theenergy which does not pass the T-R devices 51 and 52 is reflected backtoward the matched junction 43. However, when energy travels fromjunction 43 through wave guide 45 to T-R device 52 and back to junction43, it travels an odd number of half wavelengths farther than energythat travels from the junction 43 through wave guide 44 to T-R device 51and back to junction 43. The two energies which are reflected from theT-R devices 51 and 52 arrive at junction 43 in phase. This is truebecause the two energies leave junction 43 in 180 phase opposition, andthen the energy in wave guide 45 experiences an extra delay of an oddnumber of half wavelengths, and, therefore, the two energies are againin phase. Referring to Fig. 58, it is noted that this reflected energywill pass into wave guide 46 and thence to radiating device 62. Energywhich enters junction 43 from the radiating device 62 by means of guide46 divides equally and with no phase difference between the guides 44and 45. None of this energy enters wave guide 42. Normally the energyfrom the radiating device 62 is not sufficient in quantity to operatethe T-R devices 51 and 52, and thus it will all continue on to thejunction 53. The energies arrive at junction 53 in phase, since theystart from junction 43 in phase and travel equal electrical distances.At junction 53 this energy passes on into wave guide 56 and thence toreceiving device 61.

It will be obvious to those skilled in the art that the functionsperformed by the parallel and series connected branches 46 and 42 and 56and 54 may be interchanged if the interchange is made at both junctions43 and 53. The functions of the wave guide branches 46 and 42 and 56 and54 may also be interchanged at either junction 43 or 53 by properlyadjusting the relative lengths of the wave guides 4447 and 45-48.

Fig. 7 shows a device employing a matched junction in a wave guidecircuit as an impedance transformer. Because of the desirability of thematched junction, it is preferred for use in this circuit. However, thecircuit will function with junctions like the one shown in Fig. 1 if thematching irises are omitted. The impedance 71 to be transformed isconnected to a series connected wave guide 72 of a junction 77. Theimpedance 73 to which impedance 71 is to be transformed is seen whenlooking into a parallel connected wave guide 74. Two plungers 75 and 76are inserted in wave guides 81 and 82 and are adapted to be adjusted intheir relative positions. These two plungers are located at distances D1and D2, respectively, from the junction as shown in Fig. 7.

The method for determining the distances D1 and D2 is explained in thefollowing part of the specification.

In a wave guide such as wave guide 72 which is terminated by animpedance 71, which is equal to Z1, other than its characteristicimpedance Zc there exists standing waves and associated therewith astanding wave ratio SWR. The SWR is defined as the ratio of the maximumamplitude of signal along the wave guide to the minimum amplitude ofsignal along the wave guides. The maxi mum and minimum amplitudesnormally exist one fourth wavelength apart. If the impedance 71 or Z1 isdivided by Zc, the resulting quotient which is a complex notationlocates a point on an impedance circle diagram known as the Smith chart.A circle passing through this point with l+j as the center will describethe loci of all impedances existing along wave guide 72. Since wenormally desire a matched system, we wish to transform Z1 to 20. Byvariation of D1 and D2 it is possible to match any impedance Z1 to thewave guide 72 i. e. to transform it to Z0. D1 and D2, the distances fromthe center of the T-junction to the plungers 75 and 76, can be thoughtof as being determined by two parameters X and Y which are functions ofthe two impedances Z1 and 20 considered.

The following relation holds: 1 D1=X+ Y (2) D2=XY It is normallypossible to calculate or determine experimentally the SWR. If theterminating impedance Z1 and the characteristic impedance Zc are knownand both are pure resistances, then the reflection coeflicient A isgiven the junction described above gives a relationship between thereflection coefficient A and D1 and D2.

(5) A=%(1+cos However, since from Equations 1 and 2 (6) D1D2=2Y Equation5 may be solved for Y. From any arbitrary value of X, Y may be set by asystem of levers arranged to move the two plungers 75 and 76 equally inopposite directions from the center of the junction 77 or Y may be setfor each plunger separately. This will set up the proper SWR in the Waveguide containing the impedance Z1. If now we vary X, we can effectivelymove the standing waves until the actual impedance Z1 agrees with thevalue of the standing wave existing at the termination. Varying theparameter X can be thought of as rotating the Smith diagram or aseffectively lengthening the wave guide between the point of matching andthe terminating impedance Z1. A system of levers may be set up whichwill move the two plungers 75 and 76 in the same direction from thecenter of the junction and hence automatically set both plungers toconform to X.

It can be shown that any electrically symmetrical impedance transformerwhich will match any impedance to a wave guide will also match anyimpedance to any other impedance. As shown in the case above, if bothplungers 75 and 76 are changed in position by the parameter Y, the SWRonly is changed and the movement on the Smith chart is radial. If,however, we move only one plunger, the movement on the Smith chart willbe circular. If we move the other plunger, we move along anothercircular path. It is possible, therefore, by altering the twopltlllngers individually to transform any impedance to any ot er.

Referring now particularly to Fig. 8, there is shown a novel wide rangevariable attenuator designed for use in the ultra high frequency rangeand employing the matched junctions shown in Fig. 1. These matchedjunctions are preferred for use in this attenuator circuit. However, thecircuit will function with junctions in which the matching irises areomitted. A power source 81 is connected to a parallel connected waveguide 82 of a first matched junction 83. A series connected wave guide95 is terminated in an absorptive load, not shown, preferably a matchedsand load. The branches 84 and 85 of the first junction 83 areconnected, respectively, to branches 87 and 88 of a second matchedjunction 86. A variable line stretcher 91 is adapted to be a part of theenergy path through guide branches 85-88. A variable line stretcher maybe described as a section of line or wave guide whose electrical lengthis variable. A series connected wave guide 93 of the second junction 86is terminated in an absorptive load, not shown, preferably a matchedsand load. A parallel connected wave guide 92 of the junction 86 isconnected to an active load 94.

In the operation of the apparatus shown in Fig. 8, energy from powersource 81 enters wave guide 82. At the junction 83 the energy dividesinto wave guides 84 and 85 equally. Energy in wave guide 84-87 continueson to junction 86 where it is combined with energy which travels bymeans of the wave guide 85-88. The energy in wave guide 85-88, however,passes through the variable line stretcher 91 so that when it reachesthe junction 86, its phase with respect to the energy arriving throughwave guide 84-87 may differ anywhere from 0 to 360. The division ofenergy between wave guide 92 and wave guide 93 depends upon the relativephases of the two energies arriving at the junction 93. It is evident,therefore, that the amount of energy going into either wave guide 92 or93 can be controlled by adjusting the relative phases of the twoenergies arriving at the junction 86 by means of the line stretcher 91.The power source 81 and the sand load terminating guide 95 may beinterchanged without affecting the operation of the attenuator. It isalso to be understood that the line stretcher 91 may be located ineither wave guide 84-87 or wave guide 85-89 or it may be located in bothwave guides 84-87 and 85-89. Further it is understood that power source81 and active load 94 may be interchanged if desired without departingfrom the true intent of this invention.

While there has been described what is at present considered thepreferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madethereon without departing from the invention, and it is, therefore,aimed 1n the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

I claim:

An electrical device comprising a first rectangular wave gulde; a secondrectangular wave guide connected in series to a first broad wall in saidfirst guide; a third rectangular wave guide connected in parallel to thefirst narrow wall of said first wave guide and in such a manner that theaxes of said first, second and third wave guides meet in a common point;a first thin conducting plate attached to the second narrow wall andsecond broad wall of said first wave guide and extending in a planecontaining the axes of said second and third Wave guides and a secondthin plate of conducting material located in said second wave gu de andextending between the broad walls thereof and ad acent the narrow wallwhich is co-planar with the first narrow wall of the first wave guide,said plates being physically proportioned in size and so arranged in theunct1on of said first, second and third wave guides for establishing acharacteristic impedance termination for both branches of said firstwave guide, for said second wave guide and for said third wave guide attheir junction.

References Cited in the file of this patent Pound: Abstract ofapplication Serial Number 648,525, published February 20, 1951, 0. G.643. Class 178-44.

